The processes that lead to growth and differentiation in animal embryos, fetuses, neonates and juveniles share certain characteristics with the processes that lead to growth and differentiation of cell types preceding and creating tumors. Methods that recognize antigenic molecules in tumors and fetuses have shown that there are many molecules observable in both fetuses and tumors that are not observed in adult organs. In the nineteenth century it was argued that tumors might arise from residual embryonic cells in adults. Current views point to the existence of self-renewing stem cells in which genetic changes occur in lineal descent from embryonic through adult stem cells that create tumor stem cells that give rise to tumors. The summarized argument is that a single normal tissue stem cell could be the progenitor of preneoplastic lesions that in turn give rise to a founding stem cell for tumors that in turn give rise to a founding stem cell for clonal metastases and transplanted tumors. Based on the clear presence of histologically differentiable cell types in preneoplastic lesions, tumors and metastases, and by analogy to embryological growth and development, it can be inferred that the originating stem cell of tissues, preneoplastic lesions, tumors and metastases must be capable of differentiation as well as self-renewing growth. If the stem cell theory of tumor growth is correct, then there is a tremendous need to identify, sort, classify and manipulate tumor stem cells. However, identification or isolation of such cells has not been described in the art.